The use of hydrogen as a localized energy source for fuel cell powered vehicles or small electronic devices is a topic of great interest. Fuel cells are efficient, with zero point of use emissions of nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOCs), and particulate matter. Hydrogen can be extracted from sources including natural gas, water, biomass, or other more complex hydrocarbons. Despite the numerous advantages that fuel cells provide, there are significant difficulties in practice including hydrogen transportation, storage and handling. An alternative solution to problems associated with storing molecular hydrogen involves use of hydrogen stored in a liquid hydrocarbon that can be reformed on board to facilitate production of hydrogen. Methanol is an abundant commodity chemical that can be stored as a liquid at ambient temperatures and shows promise as a localized hydrogen source. Research on methanol reforming has focused primarily on four overall catalytic methanol-reforming reactions, identified in Table 1.
TABLE 1Methanol reforming reactions. All heats of reaction are in kJ/mol.ΔH(l)/EquationReactionΔH(g*)ΔH(l**)H2H2/C1CH3OH   2H2 + CO911286422CH3OH + H2O   3H2 +50131443CO23CH3OH + ½O2  −192−155−7722H2 + CO244CH3OH + ½O2 +−44238222.753H2O   11H2 + 4CO2*All species are gas phase**Includes heat of vaporization for CH3OH and H2O
The first reaction (Equation 1) is the basic methanol decomposition reaction yielding hydrogen and CO. This reaction is not suitable for fuel cell use because proton exchange membrane (PEM) cells, which use precious metals for catalysts, require hydrogen feed containing less than 50 ppm CO to avoid catalyst poisoning. Steam reforming (Equation 2) has the highest hydrogen to carbon ratio. However, this reaction is highly endothermic, not suitable for applications where a heat source is unavailable or bursts of energy may be needed. Partial oxidation (Equation 3) is exothermic, with a higher reaction rate than steam reforming and reduced tendency to form CO. Finally, combined methanol reforming (Equation 4) is a combination of steam reforming and partial oxidation. This reaction offers a balance between hydrogen to carbon ratio and heat of reaction but may be more difficult to control.